8 MASS. EXPERIMENT STATION BULLETIN 213. 



In Leaves which have been left in the Field. 



Sometimes leaves when too badly diseased are picked off and thrown 

 on the ground. At other times the whole diseased plant may be left. 

 The suckers which grow from the old stubs after a diseased crop has been 

 cut are usually infected. These are left on the field all winter. If the 

 bacteria live over in these parts, they might easil}^ start infection the fol- 

 lowing 3^ear. Being subjected to more frequent freezing and thamng and 

 other changes of weather, it is possible that they might not survive in these 

 leaves as they do in cured leaves in the tobacco sheds. We have very 

 little data bearing on this point. 



Experiment 6. — On April 24, 1922, diseased leaves, which had been cut down in 

 the fall and left in the field all winter, were collected from plants at Windsor. These 

 leaves were ground to a powder in a mortar, some of the powder was immediately 

 applied to punctured leaves in the greenhouse at Amherst, and some of it soaked 

 in water and the wet material applied after twenty-four hours to other plants. No 

 infection resulted. 



Similar tests were made with the same material by Chapman and 

 Slagg, but with negative results. This negative evidence should not be 

 considered conclusive. Further experiments are in progress. 



Clinton and McCormick (2: 376, 419) succeeded in one case in infect- 

 ing tobacco plants in the greenhouse with tobacco refuse which was win- 

 tered out of doors. 



Occurrence of Lesions on Stalks. 



Wildfire lesions have been reported previously as occurring only on the 

 leaves and occasionally on the pods. During the inspection of a field of 

 tobacco at South Amherst, some lesions which were suspected of being 

 wildfire were found on the stalks. On further examination it was found 

 that the lesions were not uncommon, but that they were present on a large 

 part of the stalks in this field. Probably they had escaped previous notice 

 because they are inconspicuous and somewhat different in appearance 

 from the lesions on the leaves. They are commonly one-eighth to one- 

 fourth inch in diameter, white, or, at most, light brown and sunken. The 

 halo is not distinct on most of them, but can be seen about some. A num- 

 ber of them were brought to the laboratory and the typical bacteria iso- 

 lated from them. Inoculation on leaves with these bacteria produced wild- 

 fire spots. In this same field and in various others examined through the 

 summer, it was also observed that lesions were common on the "ears" 

 or clasping bases of the leaves. When tobacco is stripped, these bases 

 remain mostly on the stalk. Clinton and McCormick (2: 416) inocu- 

 lated stalks and produced elongated blackened lesions. The occurrence 

 of lesions on stalks and attached leaf bases may be important in answering 

 the question as to whether land may become infested by throwing tobacco 

 stalks on it. Since the organism overwinters in the leaves, there is no 

 reason why it should not also remain alive in the stalk. 



